The main task of an ignition system is to provide a precisely timed spark with sufficient current to ignite an air fuel mixture within the engine's combustion chambers. The timing of the spark must be varied depending on a number of different operating conditions. In the past it has been a general principle that spark advance should be increased with higher engine speeds in order to optimise performance and fuel economy and decreased under heavy load conditions to avoid detonation.
A number of approaches have been taken to adjusting ignition timing in internal combustion engines. From the 1920's to the 1970's engines were equipped with point-type ignition systems. These generally made use of vacuum and centrifugal spark advance systems to advance the spark timing over a range of crankshaft RPM's. The degree of advance was a predetermined function of the physical parameters of the vacuum and centrifugal assemblies.
During the late 1970's and early 1980's, electronic ignition systems were introduced with computer-controlled spark timing. Such systems incorporate an electronic ignition module including a processor that communicates with a ROM. The ROM stores a look-up table, or “map” of predetermined spark timing values. The spark timing values are determined in the factory for each of a number of different engine operating conditions defined by variables such as throttle position, engine temperature, air temperature, cam speed and crank speed.
In use, a vehicle fitted with the electronic ignition module is also fitted with a number of sensors that monitor each of the above variables. The electronic ignition module retrieves spark timing values from the look-up table on the basis of signals from the sensors.
There are a number of problems associated with an electronic ignition system of the type described above. One of the problems is that engines rarely operate under steady state conditions when they are being driven. However, the spark timing look-up table is determined in the factory under steady-state conditions. For example, under dynamic conditions, airflow into the engine will usually be highly turbulent and unpredictable. Consequently the spark advance value that is retrieved from a factory-calibrated look-up table for a particular engine operating condition may not be optimal for an engine that is installed in a vehicle that is being driven.
A further difficulty is that the timing values stored in spark timing maps are usually somewhat conservative. This is because car-manufacturers are careful to avoid pinging and the associated risk of engine damage. Accordingly, the timing values stored in pre-calibrated maps are backed off to avoid pinging. Backing off the timing values avoids pinging but it also arrives at timing values which reduce peak engine torque output.
It is an object of the present invention to provide an engine management system that addresses the above problems.